Load balancing solution for co-operative broadcasting in a wireless communication system

ABSTRACT

The invention relates to a wireless communication system comprising a plurality of radio devices. Each radio device belongs to one or more radio neighborhoods and is capable of repeating the transmission of the broadcast message regardless of whether the radio device is operating as a router device or as a non-router device. The radio devices belonging to each radio neighborhood are configured to repeat collectively a transmission of a broadcast message a collective target amount of repetitions within each radio neighborhood. Each radio device within each radio neighborhood to which it belongs is arranged to: define a total repetition load value representing a contribution of said radio device to the collective target amount of repetitions of the broadcast message within said radio neighborhood, and decide whether to repeat the transmission of the broadcast message in accordance with the defined total repetition load value. The invention relates also to a method for the wireless communication system, a radio device for the wireless communication system, a method for the radio device, a computer program, and a tangible non-volatile computer readable medium.

PRIORITY

This application claims priority of Finnish patent application number20205077 which was filed on 27 Jan. 2020, the content of which isincorporated herein by reference.

TECHNICAL FIELD

The invention concerns in general the technical field of wirelesscommunication systems. Especially the invention concerns broadcasting inwireless cornmunication systems.

BACKGROUND

A wireless communication network, such as a wireless mesh network (WMN)or a cluster tree topology (e.g. as described in a patent publicationU.S. Pat. No. 8,064,363 B2), is formed by multiple, possibly evenhundreds or thousands or even more of radio devices that may communicatewith each other, depending on e.g. transmission range, frequency channelusage, etc. The wireless communication network may have one or more sinkdevices that may be part of gateways to other networks, e.g. Internet,and deliver data to and from the wireless communication network. Tosupport the various functions of the wireless communication networks,the radio devices typically operate in different roles. The radiodevices of the network may be divided into router devices and non-routerdevices depending on if they participate in data forwarding, i.e.routing. Router devices maintain the connectivity of the network andforward, i.e. route, data of other radio devices when needed. Non-routerdevices may transmit their own data and receive data directed for them,but they do not route data of other radio devices. Wirelesscommunication network may not be in static radio environment and part ofthe devices may move, appear or disappear.

One example of the wireless mesh network may be a wireless sensornetwork (WSN) formed by sensor devices that produce data. Each sensordevice may be equipped with one or more radios that are used to deliverthe data towards the sink device, Even if a single sensor radio cannotdirectly reach the sink device, the wireless mesh network formed betweenthe sensor radio devices takes care of it. A routing protocolimplemented in each radio device chooses the way to the sink device.Similarly, there may be data that is delivered, over multiple radiohops, from the sink device to the radio device(s) or in between radiodevices.

The data transmitted in the wireless communication network may havetight timing requirements, i.e. low latency communication requirementsfrom radio device to radio device or radio device to sink devicedelivery. As an example, in lighting system the switching control datashould be delivered over the wireless mesh network quickly, e.g. withinfew hundreds of milliseconds to create better user experience.

The data delivery should be fast, but on the other hand should not causejamming to the network. Broadcasting/flooding may be the fastest way todeliver data to multiple receivers, but it also may cause collisions andincrease interference. In case of larger networks, a non-controlledburst of broadcast messages may fully block the channels and impact thedelivery of other data. By repeating, by the router devices, thebroadcast message, the data may be distributed to the radio devices inthe network.

In broadcast communication, the trade-off between reliability andcommunication overhead may be controlled with different amount ofrepetitions of the broadcast messages. In typical broadcast/floodingcommunication protocols, the amount of repetitions is message-specificand is typically the same for every device. This means, that in denseinstallations, the total amount of repetitions may be excessive andcause a large overhead resulting in e.g. large amount of collisions andinterference. On the other hand, in sparse installation, the amount ofrepetitions may be too low to achieve sufficient reliability. Both ofthe outcomes may result in reduced quality of service, e.g. lost dataand/or increased delays.

SUMMARY

The following presents a simplified summary in order to provide basicunderstanding of some aspects of various invention embodiments. Thesummary is not an extensive overview of the invention. It is neitherintended to identify key or critical elements of the invention nor todelineate the scope of the invention. The following summary merelypresents some concepts of the invention in a simplified form as aprelude to a more detailed description of exemplifying embodiments ofthe invention.

An objective of the invention is to present a wireless communicationsystem, a method for a wireless communication system, a radio device fora wireless communication system, a method for the radio device, acomputer program and tangible non-volatile computer readable medium forco-operative broadcasting. Another objective of the invention is thatthe system, the methods, the computer program and the tangiblenon-volatile computer readable medium for co-operative broadcastingimprove the performance of the wireless communication network.

The objectives of the invention are reached by a method, an apparatusand a computer program as defined by the respective independent claims.

According to a first aspect, a wireless communication system comprisinga plurality of radio devices is provided, wherein each radio devicebelongs to one or more radio neighborhoods and is capable of repeatingthe transmission of the broadcast message regardless of whether theradio device is operating as a router device or as a non-router device,wherein radio devices belonging to each radio neighborhood areconfigured to repeat collectively a transmission of a broadcast messagea collective target amount of repetitions within each radioneighborhood, wherein each radio device within each radio neighborhoodto which it belongs is arranged to: define a total repetition load valuerepresenting a contribution of said radio device to the collectivetarget amount of repetitions of the broadcast message within said radioneighborhood, and decide whether to repeat the transmission of thebroadcast message in accordance with the defined total repetition loadvalue.

Each radio device may be associated with at least one parent device.

Moreover, the total repetition load value may be defined based on ownrepetition load value of the radio device and a parent repetition loadvalue of the radio device defined for each of the associated at leastone parent device of the radio device.

The own repetition load value of the non-router device may be zero.

The own repetition load value of the router device may depend on thenumber of router devices within the radio neighborhood and the number ofmember devices of said router device, wherein the parent repetition loadvalue of the radio device may depend on the number of router deviceswithin the radio neighborhood and the number of member devices of theassociated parent device.

Alternatively, the own repetition load value of the router device havingone or more non-router member devices may be zero, and the ownrepetition load value of the router device without non-router memberdevices may depend on the number of router devices within the radioneighborhood and the number of member devices of said radio device.

Moreover, the parent repetition load value of the router device maydepend on the number of router devices within the radio neighborhood andthe number of member devices of the associated parent device, and theparent repetition bad value of the non-router device may depend on thenumber of router devices within the radio neighborhood and the number ofnon-router member devices of the associated parent device.

Only part of the non-router devices may be arranged to participate therepetition of the transmission of the broadcast message, wherein the ownrepetition bad value of the radio device and/or the parent repetitionbad value of the radio device may further depend on the number ofparticipating non-router devices.

Each router device may be arranged to: define the number of its memberdevices and the number of its non-router member devices, and transmitregularly beacon messages, wherein each beacon message may include thecurrent number of member devices and the current number of thenon-router member devices of the router device.

Each router device may be arranged to detect the number of routerdevices within the radio neighborhood by receiving beacon messagestransmitted by other router devices of the radio neighborhood.

According to a second aspect, a method for a wireless communicationsystem comprising a plurality of radio devices is provided, wherein eachradio device belongs to one or more radio neighborhoods and is capableof repeating the transmission of the broadcast message regardless ofwhether the radio device is operating as a router device or as anon-router device, wherein radio devices belonging to each radioneighborhood are configured to repeat collectively a transmission of abroadcast message a collective target amount of repetitions within eachradio neighborhood, wherein the method comprises: defining, by eachradio device within each radio neighborhood to which it belongs, a totalrepetition load value representing a contribution of said radio deviceto the collective target amount of repetitions of the broadcast messagewithin said radio neighborhood, deciding, by each radio device withineach radio neighborhood to which it belongs, whether to repeat thetransmission of the broadcast message in accordance with the definedtotal repetition load value.

According to a third aspect, a radio device for a wireless communicationsystem is provided, wherein the radio device belongs to one or moreradio neighborhoods and is capable of repeating a transmission of abroadcast message regardless of whether the radio device is operating asa router device or as a non-router device, wherein the radio devicecomprises: a processing part, and a data transfer part for providing abi-directional radio communication with at least one other radio deviceof the system, wherein the radio device is configured to: define, by theprocessing part, a total repetition load value representing acontribution of the radio device to a collective target amount ofrepetitions of a broadcast message within each radio neighborhood; anddecide, by the processing part, whether to repeat the transmission ofthe broadcast message in accordance with the defined total repetitionload value.

According to a fourth aspect, a method for the radio device describedabove within a wireless communication system is provided, the methodcomprises: defining, by the processing part, a total repetition loadvalue representing a contribution of the radio device to a collectivetarget amount of repetitions of a broadcast message within each radioneighborhood; and deciding, by the processing part, whether to repeatthe transmission of the broadcast message in accordance with the definedtotal repetition load value.

According to a fifth aspect, a computer program is provided, wherein thecomputer program comprises instructions which, when the program isexecuted by the radio device described above, cause the radio device tocarry out at least the steps of the method for the radio devicedescribed above.

According to a sixth aspect, a tangible non-volatile computer readablemedium comprising the computer program described above is provided.

Various exemplifying and non-limiting embodiments of the invention bothas to constructions and to methods of operation, together withadditional objects and advantages thereof, will be best understood fromthe following description of specific exemplifying and non-limitingembodiments when read in connection with the accompanying drawings.

The verbs “to comprise” and “to include” are used in this document asopen limitations that neither exclude nor require the existence ofunrecited features. The features recited in dependent claims aremutually freely combinable unless otherwise explicitly stated.Furthermore, it is to be understood that the use of “a” or “an”, i.e. asingular form, throughout this document does not exclude a plurality.

BRIEF DESCRIPTION OF FIGURES

The embodiments of the invention are illustrated by way of example, andnot by way of limitation, in the figures of the accompanying drawings.

FIG. 1A illustrates schematically an example of a wireless communicationsystem according to the invention.

FIG. 1B illustrates schematically an example of a router device havingmember devices.

FIG. 2 illustrates schematically another example of a wirelesscommunication system according to the invention.

FIG. 3 illustrates schematically an example structure of a beacon frameaccording to the invention.

FIG. 4 illustrates schematically an example of a method according to theinvention.

FIGS. 5A and 5B illustrate schematically example network topologies.

FIG. 6 illustrates an example of a radio device according to theinvention.

DESCRIPTION OF THE EXEMPLIFYING EMBODIMENTS

FIG. 1A illustrates schematically an example of a wireless communicationsystem, i.e. network, 100 according to the invention. The wirelesscommunication system 100 may have a cluster tree network topology asillustrated in the example of FIG. 1A, The wireless communication system100 according to the invention may also have any other network topology,e.g. the wireless communication system may be a wireless mesh network(MN), such as a wireless sensor network (WSN).

The wireless communication system 100 according to the invention maycomprise a plurality of radio devices 102, 104 having differentoperating roles, such as router role 102 and/or non-router role 104. Therouter devices 102 of the system 100 form a skeleton for the network100, where the router devices 102 may have one or more member devices.The member devices of the router device 102 may comprise one or moreother router devices 102 and/or one or more non-router devices 104. FIG.1B illustrates an example of a router device R1 having three memberdevices: non-router member devices N3 and N4 and a router member deviceR2. The router device R1 with its member devices may be a part of awireless system 100. The system 100 according to the invention mayfurther comprise one or more radio devices operating in a sink role 106.The sink devices 106 are part of gateway to other networks, e.g.Internet, and deliver data in and from the system 100. Each radio device102, 104 of the system 100 may be associated with at least one parentdevice in their direct radio neighborhood, i.e, direct radio range.Preferably, each radio device 102, 104 of the system 100 may beassociated with one parent device at a time. This may be preferableespecially in dense wireless communication networks. However, each radiodevice 102, 104 may also be associated with more than one parent device.The parent device of each radio device 102, 104 may be a router device102. Alternatively, if the wireless communication network comprises oneor more sink devices 106, the parent device of each radio device 102,104 may be a router device 102 or a sink device 106. In the example ofFIG. 1B the router device R1 is the parent device for the router deviceR2 and for the non-router devices N3 and N4.

The term “radio neighborhood of a radio device” mean throughout thisapplication one or more radio devices whose radio transmissions may bedetected by a receiving radio device. An extended meaning of the term“radio neighborhood of a radio device” takes into account theneighbor(s) of the neighbor(s) of the radio device, i.e. multi-hopneighborhood, such as two-hop neighborhood, three-hop neighborhood,four-hop neighborhood, and/or so on. The wireless communication system100 may be such that all radio devices 102, 104 cannot communicatedirectly with the one or more sink devices 106 due to extensive distancebetween radio devices 102, 104 and the one or more sink devices 106, andlimited radio range, whereupon it is needed a multi-link, i.e. amulti-hop, communication between the radio devices 102, 104, and the oneor more sink devices 106.

One way to provide the multi-hop communication in the wirelesscommunication system 100 is broadcasting and repeating (re-broadcasting)data inside the system 100. The broadcasting may also be called asflooding. The broadcasted data may comprise for example one or morebroadcast messages. The radio devices may be disallowed to repeat thebroadcasted data multiple times, i.e, the repeating radio device 102,104 is not allowed to repeat the transmission of the same data again, ifit appears again later. For example, the data may include a uniqueidentifier (ID) to identify the data and if a radio device 102, 104receives data having ID that the radio device 102, 104 has alreadyrepeated, the radio device 102, 104 is not allowed to repeat said dataagain. For example, the ID may comprise of the original sender addressand a sequence number. In addition or alternatively, the broadcasteddata may indude a hop limit to limit the scope of the broadcasted data.For example, the sender may set the hop limit for the broadcasted data,and each radio device 102, 104 repeating the data may decrement the hoplimit value. When the radio device 102, 104 receives data with hop limitvalue of zero, it will not repeat the data.

The term broadcast refers to a communication method not destinationaddressing. By broadcasting and repeating the data may be distributed tothe radio devices 102, 104 of the system 100. The radio devices 102, 104that the data may actually be targeted to may be identified by separateaddressing. The separate addressing may include for example broadcastaddressing, where the data may be destined to all the radio devices 102,104 of the system 100, multicast addressing, where the data may bedestined to a group of radio devices 102, 104 of the system 100, orunicast addressing where the data may be destined to a single radiodevice 102, 104 of the system 100.

FIG. 2 schematically illustrates an example of the wirelesscommunication system 100 comprising a plurality of radio devices 102,104 each belonging to one or more radio neighborhood, i.e. radio range200. In the example of FIG. 2 the one or more radio neighborhoods 200are overlapping, i.e. each radio neighborhood 200 comprises one or moreradio devices 102 belonging to one or more other radio neighborhoods200. The transmission of broadcast messages of the radio devices 102,104 belonging to more than one radio neighborhood 200 may be heard, i.e.received, inside more than one radio neighborhood 200 enabling multi-hopcommunication. The example wireless communication system 100 of FIG. 2comprises only router devices 102 and non-router devices 104, but thewireless communication system 100 may further comprise one or more sinkdevices 106 each belonging to one or more radio neighborhood 200.

Typically, in known wireless communication networks only the routerdevices 102 participate in forwarding, i.e. routing, of the broadcastmessages and the non-router devices 104 may transmit their own data andreceive data directed for them, but the non-router devices 104 do notparticipate in routing the broadcast messages. For example, in manypractical multi-hop networks, e.g. lighting control networks, there maybe plenty of mains powered non-router devices 104 that are notparticipating in the routing activities. However, each radio device 102,104 of the wireless communication system 100 according to the presentinvention is capable of repeating a transmission of a broadcast messagethat is aimed to be delivered in the system 100 regardless of whetherthe radio device 102, 104 is operating as a router device 102 or as anon-router device 104. In other words, each radio device 102, 104 of theplurality of radio devices of the wireless communication system 100according to the invention may participate in routing of a broadcastmessage that is aimed to be delivered in the system 100. This enablesthat the possible other resources of the wireless communication system100 may be taken into use to reduce the duty from the router devices102, which improves the data routing performance of the system 100, itslatency and throughput that is primarily dependent on the router devices102. The one or more sink devices 106 do not participate the repetitionof the transmission of the broadcast message.

In order to distribute a broadcast message inside the wirelesscommunication system 100 according to the invention, the radio devices102, 104 belonging to each radio neighborhood 200 are configured torepeat collectively, i.e. cooperatively, a transmission of a broadcastmessage a collective target amount of repetitions within each radioneighborhood 200. The collective target amount of repetitions of thetransmission of the broadcast message within each neighborhood may bee.g. a predefined amount, defined during the run-time of the method, orset by the application, wherein the wireless communication system 100may be implemented. The target is to locally, i.e. within each radioneighborhood 200, provide the collective target amount of repetitions ofthe transmission of the broadcast message independent of the localnumber of router devices 102 and non-router devices 104, i.e. the numberof router devices 102 and the number of non-router devices 104 withineach radio neighborhood 200, i.e. radio range. In other words, thetarget is to keep the local collective target amount of repetitions ofthe transmission of the broadcast message the same inside each radioneighborhood 200 independent of the amount of router devices 102 insideeach radio neighborhood. In other words, the more router devices 102 arewithin each radio neighborhood 200, the less repetitions of thetransmission of the broadcast message are needed per router device 102.Each router device 102 may detect a router count (R), i.e. the number ofrouter devices 102, within each radio neighborhood 200 to which therouter device 102 belongs by scanning transmissions, e.g. beaconmessages, within the radio neighborhood 200. Similarly, each non-routerdevice 104 may detect the router count (R), i.e. the number of routerdevices 102 within the radio neighborhood 200, by scanningtransmissions, e.g. beacon messages, within each radio neighborhood 200to which the non-router device 104 belongs. In other words, each routerdevice 102 and each non-router device 104 may be arranged to detect thenumber of router devices 102 within its radio neighborhood 200 byreceiving beacon messages transmitted by other router devices 102 withinthe radio neighborhood 200.

Furthermore, each router device 102 may define, e.g, keep track of, thenumber of its member devices, i.e. member count, (M) and the number ofits non-router member devices, i.e. non-router member count, (N).Moreover, each router device 102 may report the member count (M) and thenon-router member count (N) to the members or said router device 102.The reporting may for example be implemented as a part of regularlydistributed, i.e. transmitted, beacon messages, i.e. beacon frames 300.Each transmitted beacon message transmitted by the router device 102 mayinclude the number of the member devices (M) of the router device 102and the number of the non-router member devices (N) of the router device102. FIG. 3 illustrates an example structure of a beacon frame 300including the number of the member devices (M) and the number of thenon-router member devices (N), The number of the member devices (M)field 310 and the number of the non-router member devices (N) field 312may be included in a medium access control layer (MAC) payload field 306of the beacon frame 300. The beacon frame may further comprise e.g.physical layer (PHY) header field 302, MAC header field 304, and PHYfooter field 308.

A load balanced collective broadcast method according to the inventionis described next referring to FIG. 4, which schematically illustratesan example of the invention as a flow chart. The method is described byreferring to one radio device 102, 104 within one radio neighborhood 200to which said one radio device 102, 104 belongs. However, each radiodevice 102, 104 of the system 100 that receives a broadcast messageinside the radio neighborhood 200 may independently perform the methodsteps. In other words, each radio device 102, 104 that receives abroadcast message may be configured to indedecide whether to repeat thetransmission of the received broadcast message or not and the amount ofrepetitions of the transmission of the broadcast message by performingat least some of the steps of the method according to the invention.Moreover, each radio device 102, 104 may independently perform themethod steps within each radio neighborhood 200 to which each radiodevice 102, 104 belongs.

The radio device 102, 104 may listen, i.e. scan, transmissions withinthe radio neighborhood 200 at a step 402 in order to receive thebroadcast message at a step 404. If the radio device 102, 104 detects ata step 404 that it does not receive any broadcast messages it continueslistening transmissions at the step 402.

At a step 406 the radio device 102, 104 defines a total repetition loadvalue, after receiving the broadcast message. The total repetition loadvalue represents the contribution of said radio device 102, 104 to thecollective target amount of repetitions of the broadcast message withinthe radio neighborhood 200, The total repetition load value may bedefined based on an own repetition load value of the radio device 102,104 and a parent repetition load value of the radio device 102, 104defined for each of the at least one associated parent device of theradio device 102, 104 as will be described later by referring differentexamples.

At a step 408 the radio device 102, 104 decides whether to repeat thetransmission of the broadcast message in accordance with the definedtotal repetition load value, i.e. based on the defined total repetitionload value. The total repetition load value defines a probability withwhich the radio device 102, 104 repeats the transmission the broadcastmessage and the amount of repetitions so that the collective targetamount is achieved. In other words, the radio device 102, 104 decidesbased on the defined total repetition load value whether it repeats thebroadcast message and how many times it repeats the broadcast message.The amount of repetitions of individual radio device 102, 104 may differfrom 0 to n, wherein n>0, in order to achieve the collective targetamount of repetitions inside the radio neighborhood.

The repetition of the broadcast message may be performed on one or morefrequency channels. The one or more frequency channels may for examplebe pre-defined or defined during the run-time of the method by the radiodevice 102, 104. The collective target amount of repetitions of thebroadcast message may be the same or different for each of the one ormore frequency channels. Alternatively or in addition, the collectivetarget amount of repetitions of the broadcast message and/or the one ormore frequency channels may be the same or different for each radioneighborhood 200.

As described above the total repetition load value (TRL) may be definedbased on the own repetition load value (ORL) of the radio device 102,104 and the parent repetition load value (PRL) of the radio device 102,104 defined for each of the associated at least one parent device of theradio device 102, 104. For example, the total repetition load value maybe defined to be the sum of the own repetition load value of the radiodevice 102, 104 and the parent repetition load value(s) of the radiodevice 102, 104 defined for each of the associated at least one parentdevice. If the radio device 102, 104 is associated with more than oneparent device, the parent repetition load value (PRL) of the radiodevice 102, 104 is defined for each parent device of the radio device102, 104 and the total repetition load value (TRL) may be defined to bethe sum of the own repetition load value (ORL) of the radio device 102,104 and the parent repetition load values (PRLs) of the radio device102, 104 defined for each parent device of the radio device 102, 104.Alternatively, if the radio device 102, 104 is associated with oneparent device, the parent repetition load value (PRL) of the radiodevice 102, 104 is defined for said one parent device of the radiodevice 102, 104 and the total repetition load value (TRL) may be definedto be the sum of the own repetition load value (ORL) of the radio device102, 104 and the parent repetition load value (PRL) of the radio device102, 104 defined for said one parent device.

As discussed above, the sink devices 106 do not repeat the transmissionof the broadcast message. Thus, the own repetition load value (ORL) ofthe sink device 106 is zero and the parent repetition load value (PRL)of the sink device 106 is zero causing that the total repetition loadvalue (TRL) of the sink device 106 is zero. Moreover, if a sink device106 is the parent of the radio device 102, 104, the parent repetitionload value (PRL) of the radio device 102, 104 defined for the sinkdevice 106 is zero, because the sink devices 106 do not repeat thetransmission of the broadcast message.

Next some examples for defining the own repetition load value (ORL) ofthe radio device 102, 104 and the parent repetition load value (PRL) ofthe radio device 102, 104 are described.

According to a first example, the broadcast message repetition load maybe divided between the router devices 102 and the non-router device 104within the radio neighborhood 200 by applying distributed decisionmaking. The own repetition load value may be defined to be zero for thenon-router devices 104. Moreover, the own repetition load of the routerdevice 102 may depend on the number of router devices 102 within theradio neighborhood 200 and the number of member devices of said routerdevice 102. The own repetition load value (ORL) of the router device 102may be defined for example according to the following formula:

ORL=1/(R×(M+1)),  (1)

wherein R is number of router devices 102 within the radio neighborhood200, i.e. router count, and M is the number of the member devices ofsaid router device 102, i.e. the member count of said router device 102.

The parent repetition load value (PRL) of the radio device 102, 104 maydepend on the number of router devices within the radio neighborhood 200and the number of member devices of the associated parent device of theradio device 102, 104 irrespective whether the radio device 102, 104 isoperating as a router device 102 or as a non-router device 104, Theparent repetition load value of the radio device 102, 104 may be definedfor example according to the following formula:

PRL==1/(R×(M _(P)+1)),  (2)

wherein R is number of router devices 102 within the radio neighborhood,i.e. router count, and M_(P) is the number of the member devices of theassociated parent device, i.e. the member count of the associated parentdevice. As discussed above, if the radio device 102, 104 has more thanone parent device, the parent repetition load value (PRL) may be definedseparately for each associated parent device of the radio device 102,104 with the above formula (2).

According to a second example, the broadcast message repetition load maybe divided between the router devices 102 and the non-router device 104within the radio neighborhood 200 by applying non-equal load balanceddecision making. In this example the broadcast message repetition loadmay be moved from the router devices 102 to their non-router device 104members, if the router device 102 has one or more non-router devicemembers 104.

Also, in this example the own repetition load value (ORL) may be definedto be zero for the non-router devices 104. The own repetition load value(ORL) of the router devices 102 depends on whether the router device 102has one or more non-router member devices 104. The own repetition loadvalue may be defined to be zero for the router devices 102 having one ormore non-router members devices 104. The own repetition load value ofthe router device 102 without non-router member devices 104 may dependon the number of router devices 102 within the radio neighborhood 200and the number of member devices of said radio device 102, 104. The ownrepetition load value (ORL) of the router devices 102 without non-routermember devices 104 may be defined for example according to the sameformula (1) as in the first example described above.

In this second example, the parent repetition load value (PRL) may bedefined differently for the router devices 102 than for the non-routerdevices 104. The parent repetition load value (PRL) of the non-routerdevice 104 may depend on the number of router devices 102 within theradio neighborhood and the number of non-router member devices 104 ofthe associated parent device. The parent repetition load value of thenon-router device 104 may be defined for example according to thefollowing formula:

PRL=1/(R×N _(P)),  (3)

wherein R is number of router devices 102 within the radio neighborhood,i.e. router count, and N_(P) is the number of the non-router memberdevices 104 of the associated parent device, i.e. the non-router membercount of the associated parent device. As discussed above, if thenon-router device 104 has more than one parent device, the parentrepetition load value (PRL) may be defined separately for eachassociated parent device of the non-router device 104 with the aboveformula (3).

The parent repetition bad value (PRL) of the router devices 102 maydepend on the number of router devices within the radio neighborhood 200and the number of member devices of the associated parent device of therouter device 102. The parent repetition bad value (PRL) of the routerdevice 102 may be defined according to the same formula (2) as in thefirst example described above. However, if the parent device of therouter device 102 has one or more non-router member devices 104, theparent repetition bad value (PRL) of the router devices 102 is zero.

FIGS. 5A and 5B illustrate example network topologies comprising onesink device S, 106, three router devices R1-R3, 102 and three non-routerdevices N4-N6, 104. Each radio device 102, 104 of the example networktopologies of FIGS. 5A and 5B belong to one radio neighborhood 200. Theexample network topologies of FIGS. 5A and 5B differ slightly from eachother. In the example network topology of FIG. 5A the router device R2has three members: router device R3, non-router device N5 and non-routerdevice N6, and the router device R3 does not have any members. In theexample network topology of FIG. 5B the router device R2 has twomembers: router device R3 and non-router device N5, and the routerdevice R3 has one member that is non-router device N6.

As discussed above each radio device 102, 104 of the example networktopologies of FIGS. 5A and 5B defines independently its total repetitionload value and decides independently whether to repeat the transmissionof the broadcast message in accordance with the defined total repetitionload value. To define the total repetition load value each radio device102, 104 may define its own repetition load value and its parentrepetition load value of radio device 102, 104 defined for each of theat least one parent device. In the example network topologies of FIGS.5A and 5B each radio device 102, 104 is associated with one parentdevice. Thus, the total repetition load value (TRL) of each radio device102, 104 is the sum of the its own repetition load value (ORL) and itsparent repetition load value (PRL) defined for said one parent device,Table 1 presents load values (ORL, PRL and TRL) for each radio device102, 104 of the example network topology of FIG. 5A defined according tothe first example discussed above. As can be seen from the defined totalrepresentation load values of the Table 1 the probability that therouter device R3, which has no member devices, repeats the transmissionof the broadcast message is 42%, whereas the probability that thenon-router devices N5 and/or N6 repeat the transmission of the broadcastmessage is only 8%.

TABLE 1 The defined load values (ORL, PRL and TRL) for each radio deviceof the example network topology FIG. 5A for the first example. Radiodevice ORL PRL TRL (%) Comments S 0 0 0 Does not repeat R1 1/(3*2) 0 17% Has one member and parent is sink that does not repeat R2 1/(3*4)1/(3*2)  25% Has three members R3 1/3 1/(3*4)  42% No members N4 0 0 0Parent is sink that does not repeat N5 0 1/(3*4)  8% N6 0 1/(3*4)  8%SUM 100%

Table 2, in turn, presents load values (ORL, PRL and TRL) for each radiodevice 102, 104 of the example network topology of FIG. 5B definedaccording to the first example discussed above. As can be seen from thedefined total representation load values of the Table 2 the probabilitythat the router device R3, which now has one member device, repeats thetransmission of the broadcast message is now 28%, whereas theprobability that the non-router devices N5 and N6 repeat thetransmission of the broadcast message is 11% and 17%, respectively.Thus, the probability that the non-router devices N5 and N6 participatein the routing, i.e. repetition of the broadcast message, is higher inthe example network topology of FIG. 5B than in the example networktopology of FIG. 5A.

TABLE 2 The defined load values (ORL, PRL and TRL) for each radio deviceof the example network topology of FIG. 5B for the first example. Radiodevice ORL PRL TRL (%) Comments S 0 0 0 Does not repeat R1 1/(3*2) 0 17% Has one member and parent is sink that does not repeat R2 1/(3*3)1/(3*2)  28% Has two members R3 1/(3*2) 1/(3*3)  28% Has one member N4 00 0 Parent is sink that does not repeat N5 0 1/(3*3)  11% N6 0 1/(3*2) 17% SUM 100%

Table 3, in turn, presents load values (ORL, PRL and TRL) for each radiodevice 102, 104 of the example network topology of FIG. 5A definedaccording the second example discussed above. As can be seen from thedefined total representation load values of the Table 3 the probabilitythat the router device R2, which has two non-router member devices N5and N6 and one router member device, repeats the transmission of thebroadcast message is now 1% and the probability that the non-routerdevices N5 and N6 repeat the transmission of the broadcast message is17%. This means that broadcast repetition load of the router device R2is moved partly to its non-router member devices N5 and N6, i.e. each ofthe non-router members N5 and N6 takes ½ of the load of the parentdevice. Moreover, the broadcast repetition load of the router device R3,which has no member devices is also moved partly to the non-routingmembers N5 and N6 of the router device R2, which is the parent device ofthe router device R3. When comparing the results of the Table 3, inwhich the load values (ORL, PRL and TRL) of the example network topologyof FIG. 5A are defined for the second example above, to the results ofthe Table 1, in which the load values (ORL, PRL and TRL) of the examplenetwork topology of FIG. 5A are defined according to the first exampleabove, it may be seen the difference between the non-equal load balanceddecision making (second example) and the distributed decision making(first example).

TABLE 3 The defined load values (ORL, PRL and TRL) for each radio deviceof the example network topology of FIG. 5A for the second example. Radiodevice ORL PRL TRL (%) Comments S 0 0 0 Does not repeat R1 1/(3*2) 0 17% Has one router member and parent is sink that does not repeat R2 01/(3*2)  17% Has one router member and two non-router members R3 1/3 0 33% No members N4 0 0 0 Parent is sink that does not repeat N5 01/(3*2)  17% N6 0 1/(3*2)  17% SUM 100%

In the above presented examples all the radio devices 102, 104 of thesystem 100 may participate in the repetition of the transmission of thebroadcast message, but the invention is not limited to that, Accordingto an example embodiment of the invention only part of the non-routerdevices 104 may be arranged to participate the repetition of thetransmission of the broadcast message. For example, at least part of thenon-router devices 104 of the system 100 may be battery powered andshould not preferably consume their energy resources for the repetitionof the transmission of the broadcast messages. Thus, the own repetitionload value (ORL) of the radio device 102, 104 and the parent repetitionload value (PRL) of the radio device 102, 104 may further depend on thenumber of participating non-router member devices (QM), i.e. qualifiednon-router member devices 104. The router device 102 having one or morenon-router member device 104 may inform all its member device about thenumber of the participating non-router member devices (QM).

The number of participating non-router member devices (QM) may beincluded in the definitions of the own repetition load value (ORL) ofthe radio device 102, 104 and the parent repetition load value (PRL) ofthe radio device 102, 104 according to the above presented examples.

For example, in the definition according to the first example, the ownrepetition load value (ORL) of the router device 102 may be defined forexample instead of the formula (1) according to the following formula:

ORL=1/(R×(QM+1)),  (4)

wherein R is number of router devices 102 within the radio neighborhood200, i.e. router count, and QM is the number of the participatingnon-router member devices of said router device 102.

Alternatively or in addition, in the definition according to the firstexample, the parent repetition load value (PRL) of the radio device 102,104 may be defined for example instead of the formula (2) according tothe following formula:

PRL=1/(R×(QM _(P)+1)),  (5)

wherein R is number of router devices 102 within the radio neighborhood200, i.e. router count, and QM_(P) is the number of the participatingnon-router member devices of the associated parent device.

Alternatively or in addition, in the definition according to the secondexample, the parent repetition load value (PRL) of the non-router device104 may be defined for example instead of the formula (3) according tothe following formula:

PRL=1/(R×(N _(P)−(M _(P) −QM))),  (6)

wherein R is number of router devices 102 within the radio neighborhood,i.e. router count, and N_(P) is the number of the non-router memberdevices 104 of the associated parent device, i.e. the non-router membercount of the associated parent device, M_(P) is the number of the memberdevices of the associated parent device, i.e. the member count of theassociated parent device, and QM_(P) is the number of the participatingnon-router member devices of the associated parent device.

Above, only non-limiting examples for definition of the own repetitionload value (ORL) of the radio device 102, 104 and the parent repetitionload value (PRL) of the radio device 102, 104 are disclosed. Theinvention is not limited to the above present examples and the ownrepetition load value (ORL) of the radio device 102, 104 and/or theparent repetition load value (PRL) of the radio device 102, 104 may bedefined in any other way. The above presented examples disclose simpleways to define the own repetition load value (ORL) of the radio device102, 104 and the parent repetition load value (PRL) of the radio device102, 104 which decreases the needed processing capacity.

FIG. 6 illustrates an example of a radio device (apparatus) 102, 104according to the invention. The radio device 102, 104 comprises aprocessing part 602 that is configured to perform user and/or computerprogram (software) initiated instructions, and to process data in orderto run an application and communication protocol. The processing part602 may comprise at least one processor, e.g. one, two, or threeprocessors. The radio device 102, 104 further comprises a memory part604 in order to store and to maintain data. The data may beinstructions, computer programs, and data files. The memory part 604 maycomprise at least one memory, e.g. one, two, or three memories.

The radio device 102, 104 further comprises a data transfer part 606 andan antenna part 608 for providing a bi-directional radio communicationwith at least one other radio device 102, 104. The radio device 102, 104may use the data transfer part 606 in order to transmit commands,requests, messages, and data to at least one of other radio devices 102,104, 106 of the wireless communication system 100 via the antenna part608. The data transfer part 606 also receives commands, requests,messages, and data from at least one of the other radio devices 102,104, 106 via the antenna part 608 in the wireless communication system100. The radio device 102, 104 may further comprise a power supply part610. The power supply part 610 comprises components for powering theradio 102, 104, e.g. a battery and a regulator.

The memory part 602 comprises a data transfer application for operating,i.e. controlling, the data transfer part 606, an antenna application foroperating the antenna part 608, and a power supply application foroperating the power supply part 610.

The memory part 604 comprises also load balancing application 605, i.e.a computer program, comprising instructions which, is configured to useat least one of parts 606, 608, 610 in order to perform, i.e. carry out,at least the operations, i.e. the method steps, of the radio device 102,104 described above in this description part and figures, when it isrun, i.e. executed, by a computer, e.g. by the radio device 102, 104 bymeans of the processing part 602.

The computer program may be stored in a tangible non-volatile computerreadable medium, e.g. an USB stick or a CD-ROM disc.

The method, the wireless communication system 100, and the radio device102, 104 according to the invention described above improves theperformance of the wireless communication network 100 by distributing,i.e. offloading, broadcasting duties also to “idle” radio devices, i.e.radio devices that do not typically participate in broadcasting, e.g.non-router devices 104. The invention enables simple way for each radiodevice 102, 104 to define themselves the amount of offloading they aresupposed to do with minimal negotiations, i.e. the radio devices do noneed to send separate messages to request the information needed todefine the need to repeat the transmission of the broadcast message.Moreover, the invention described above enables that a broadcast messagemay be delivered within the wireless communication system 100 bydecreasing the amount of unnecessary traffic and collisions in thewireless communication system 100.

The specific examples provided in the description given above should notbe construed as limiting the applicability and/or the interpretation ofthe appended claims. Lists and groups of examples provided in thedescription given above are not exhaustive unless otherwise explicitlystated.

1. A wireless communication system comprising a plurality of radiodevices, each radio device belongs to one or more radio neighborhoodsand is capable of repeating the transmission of the broadcast messageregardless of whether the radio device is operating as a router deviceor as a non-router device, wherein radio devices belonging to each radioneighborhood are configured to repeat collectively a transmission of abroadcast message a collective target amount of repetitions within eachradio neighborhood, wherein each radio device within each radioneighborhood to which it belongs is arranged to: define a totalrepetition load value representing a contribution of said radio deviceto the collective target amount of repetitions of the broadcast messagewithin said radio neighborhood, and decide whether to repeat thetransmission of the broadcast message in accordance with the definedtotal repetition load value.
 2. The system according to claim 1, whereineach radio device is associated with at least one parent device.
 3. Thesystem according to claim 2, wherein the total repetition load value isdefined based on an own repetition load value of the radio device and aparent repetition load value of the radio device defined for each of theassociated at least one parent device of the radio device.
 4. The systemaccording to claim 3, wherein the own repetition load value of thenon-router device is zero.
 5. The system according to claim 3, whereinthe own repetition load value of the router device depends on the numberof router devices within the radio neighborhood and the number of memberdevices of said router device, wherein the parent repetition load valueof the radio device depends on the number of router devices within theradio neighborhood and the number of member devices of the associatedparent device.
 6. The system according to claim 3, wherein the ownrepetition load value of the router device having one or more non-routermember devices is zero, and wherein the own repetition load value of therouter device without non-router member devices depends on the number ofrouter devices within the radio neighborhood and the number of memberdevices of said radio device.
 7. The system (according to claim 6,wherein the parent repetition load value of the router device depends onthe number of router devices within the radio neighborhood and thenumber of member devices of the associated parent device, and whereinthe parent repetition load value of the non-router device depends on thenumber of router devices within the radio neighborhood and the number ofnon-router member devices of the associated parent device.
 8. The systemaccording to claim 3, wherein only part of the non-router devices arearranged to participate the repetition of the transmission of thebroadcast message; wherein the own repetition load value of the radiodevice and/or the parent repetition load value of the radio devicefurther depend on the number of participating non-router devices.
 9. Thesystem according to claim 1, wherein each router device is arranged to:define the number of its member devices and the number of its non-routermember devices, and transmit regularly beacon messages, wherein eachbeacon message includes the current number of member devices and thecurrent number of the non-router member devices of the router device.10. The system according to claim 1, wherein each router device isarranged to detect the number of router devices within the radioneighborhood by receiving beacon messages transmitted by other routerdevices of the radio neighborhood.
 11. A method for a wirelesscommunication system comprising a plurality of radio devices, each radiodevice belongs to one or more radio neighborhoods and is capable ofrepeating the transmission of the broadcast message regardless ofwhether the radio device is operating as a router device or as anon-router device, wherein radio devices belonging to each radioneighborhood are configured to repeat collectively a transmission of abroadcast message a collective target amount of repetitions within eachradio neighborhood, wherein the method comprises: defining, by eachradio device within each radio neighborhood to which it belongs, a totalrepetition load value representing a contribution of said radio deviceto the collective target amount of repetitions of the broadcast messagewithin said radio neighborhood; and deciding, by each radio devicewithin each radio neighborhood to which it belongs, whether to repeatthe transmission of the broadcast message in accordance with the definedtotal repetition load value.
 12. A radio device for a wirelesscommunication system, wherein the radio device belongs to one or moreradio neighborhoods and is capable of repeating a transmission of abroadcast message regardless of whether the radio device is operating asa router device or as a non-router device, wherein the radio devicecomprises: a processing part, and a data transfer part for providing abi-directional radio communication with at least one other radio deviceof the system, wherein the radio device is configured to: define, by theprocessing part, a total repetition load value representing acontribution of the radio device to a collective target amount ofrepetitions of a broadcast message within each radio neighborhood; anddecide, by the processing part, whether to repeat the transmission ofthe broadcast message in accordance with the defined total repetitionload value.
 13. A method for the radio device according to claim 12within a wireless communication system, the method comprises: defining,by the processing part, a total repetition load value representing acontribution of the radio device to a collective target amount ofrepetitions of a broadcast message within each radio neighborhood; anddeciding, by the processing part, whether to repeat the transmission ofthe broadcast message in accordance with the defined total repetitionload value.
 14. A computer program comprising instructions which, whenthe program is executed by the radio device according to claim 12, causethe radio device to carry out at least the steps of the method accordingto claim
 13. 15. A tangible non-volatile computer readable mediumcomprising the computer program according to claim 14.